The invention relates to an apparatus in spinning preparation for separating foreign objects at a high-speed roll for opening or doffing fibre material, for example, cotton, synthetic fibres or the like.
It is known to provide at least one device for separating the foreign objects associated with the clothed face of the opening roll or doffer roll, which device comprises an arrangement for producing a current of blast air that flows in the direction onto the clothed face and generates an air stream that detaches the foreign objects from the clothed face and carries the foreign objects away, the arrangement comprising a plurality of blast nozzles that are arranged across the width of the opening roll or doffer roll and are connected to a compressed air pipe and to valves.
In the case of a known apparatus (DE-A-196 45 844), two slow-speed feed rolls are associated with the opening roll laterally and horizontally and feed the fibre material to the opening roll. To keep the evelope of co-rotating air on the opening roll, guide plates are provided. At the lower end of the opening roll there is an arrangement (sensors) for optical detection of foreign particles in the fibre tufts, which is located in a collecting area for separated particles. Between the guide plate and a blade there is an opening though which a current of blast air is directed obliquely from below briefly onto that area of the roll surface where the fibre tufts contain unwanted foreign particles. In this way, the contaminated fibre tufts are blown off the roll surface and then carried away. The drawback of this apparatus is the considerable space requirement, which is caused inter alia by the blowing direction of the blast air source (air nozzles) in the area beneath the opening roll. In addition, it is inconvenient that the blast air source and the valves are located freely in the waste collecting area, which leads to considerable interference to operation, interruptions and the like. Another disadvantage is that the air nozzles with the magnetic valves are arranged separately across the width of the roll. The air jet of each individual air nozzle is therefore directed either tangentially, or slightly away from this tangent, away from the opening roll. A consistent quality of separation and a rapid adjustment when the processed fibre material is changed to one with different proportions of foreign objects is not possible with this apparatus.